fix(cli): add popularities to "yarn start" script

[caugner]

Summary

Related to: #10653 (comment)

Problem

yarn start fails on a fresh checkout, with the following error:

error: ENOENT: no such file or directory, open '/path/to/yari/popularities.json'

Solution

Run yarn tool popularities as part of yarn start, if the popularities.json doesn't exist.

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How did you test this change?

Ran yarn start on a fresh checkout, and I was able open http://localhost:3000/ afterwards.

[caugner]

Self-approval, as the fix is trivial.